1. Field of the Invention
The present invention relates to a polyester container and a process for producing the same. More particularly, the present invention relates to a polyester container having a high crystallinity and excellent transparency and thermal distortion resistance even in a heating atmosphere of a high temperature and to a process for producing the same.
2. Prior Art
In recent years, polybutylene terephthalate (PBT) has also been widely used in the field of packaging wherein the package comes into contact with chemicals and foods, because it is excellent in the mechanical properties and in the chemical resistance, resistance to permeation by gas and thermal resistance.
The PBT, however, brings about whitening upon being thermoformed due to its high crystallinity, so that a container having excellent transparency cannot be produced from the PBT.
It is possible to enhance the transparency and lower the crystallinity of the PBT through the introduction of other structural units in the polymer per se to prepare a copolymer. Containers produced by this technique, however, promote crystallization upon being heated and are likely to become opaque. Further, when the copolymer is amorphous as a whole, the properties inherent in the PBT are lost and in particular the strength and thermal resistance are remarkably deteriorated.
Thus it is very difficult for containers produced by the thermoforming of PBT or a copolymer of PBT to have excellent properties derived from the crystallinity, particularly both of thermal resistance and persistent transparency. Therefore, a container having both the above-described properties has earnestly been desired in the art.